Optical pickup device and recording and/or reproducing apparatus

ABSTRACT

An optical pickup device includes an objective lens ( 2 ), with a numerical aperture (NA) being not less than 1, having a solid immersion lens ( 1 ) which is made up by a spherical portion ( 1   a ) and a flat portion ( 1   b ) parallel to a surface ( 101   a ) of an optical disc ( 101 ). The component of the reflected light from the optical disc in the polarized state perpendicular to the polarized state of the reflected light which prevails when the distance between the surface of the optical disc and the flat portion of the solid immersion lens is zero is detected. The so detected light intensity is associated with the distance between the optical disc surface and the solid immersion lens to accurately detect the minute gap between the optical disc and the solid immersion lens.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and is based upon and claims thebenefit of priority under 35 U.S.C. §120 for U.S. Ser. No. 10/415,103,filed Apr. 30, 2003, and claims the benefit of priority under 35 U.S.C.§ 119 from a PCT Application No. PCT/JP02/08627, filed Aug. 27, 2002,the entire contents of each which are incorporated herein by reference.

TECHNICAL FIELD

This invention relates to an optical pickup device for reading outinformation signals recorded on an optical recording medium, such as anoptical disc, and to a recording and/or reproducing apparatus providedwith this optical pickup device. More particularly, it relates to anoptical pickup device and a recording and/or reproducing apparatusconfigured for controlling the distance between an objective lens of theoptical pickup device and an optical recording medium.

BACKGROUND ART

Currently, a large variety of optical recording mediums are in use.Typical of these are optical discs, such as a CD (Compact Disc) or a DVD(Digital Versatile Disc), and magneto-optical discs. The informationsignals, recorded on the optical disc of this type, are read out bycondensing the light beam, radiated by a light source, provided in theoptical pickup device, by an objective lens, illuminating the light beamto a signal recording surface of the optical disc and by detecting thelight beam reflected back from the signal recording surface by aphotodetector. It is noted that the information signals, recorded on theCD or on the DVD, are read out by detecting changes in reflectivity ofthe light beam, reflected back from the signal recording surface, by thephotodetector. In the case of the magneto-optical disc, the informationsignals are read out by detecting the Kerr rotation of the light beamreflected from the signal recording surface of the disc.

The information signals recorded on the above-described optical disc areread out at least as the objective lens condensing the light beamradiated from the light source is kept out of contact with the opticaldisc.

The light spot of the light beam, condensed on the signal recordingsurface of the optical disc by the objective lens of the optical pickupdevice, is approximately given by λ/NA, where λ is the wavelength of theilluminated light beam and NA is the numerical aperture. The resolutionis also proportionate to this value.

Meanwhile, the following equation holds for NA:NA=n≅sin θwhere n is the refractive index of the medium and θ is the angle of theambient light incident on the objective lens.

If the medium is air, the value of NA cannot exceed 1 (unity). As atechnique for a case in which this limit value is exceeded, an opticalpickup device employing a solid immersion lens has been proposed (I.Ichimura et al., ?Near-Field Phase-Change Optical Recording of 1.36Numerical Aperture≅, Jpn. J. Appl. Phys. vol. 39, 962-967, 2000).

The solid immersion lens is formed of a material of the same refractiveindex as the optical disc substrate, and is made up by a sphericalportion, forming a fraction of a sphere, and a flat portion facing theoptical disc surface. The solid immersion lens, used in an opticalpickup device, is used as the flat portion kept extremely close to theoptical disc surface. The boundary surface between this solid immersionlens and the optical disc is traversed by an evanescent wave. It is thisevanescent wave that reaches the signal recording surface of the opticaldisc.

When the information signals, recorded on the optical disc, are read outusing this optical pickup device, a suitable gap needs to be providedbetween the rotationally driven optical disc and the solid immersionlens forming the objective lens. Since the gap as the air layer isprovided between the optical disc and the solid immersion lens, anevanescent wave must be used in order to make the numerical aperture(NA) of the objective lens larger than 1 (unity). The evanescent wave isattenuated exponentially as from the boundary surface. It is thereforenecessary that the gap between the optical disc and the solid immersionlens shall be of an extremely small value on the order of one-tenth ofthe light emission wavelength λ of the light source provided on theoptical pickup device, while it is necessary that the solid immersionlens shall be close to the signal recording surface.

For controlling the gap in this manner, a servo method has so far beenproposed in which an electrode is formed on the surface of the solidimmersion lens, the capacitance across the electrode and the opticaldisc is detected to derive a gap error signal, and in which the distancebetween the solid immersion lens and the optical disc is controlledbased on this error signal.

For implementing this method, it is necessary to form the electrode onthe surface of the solid immersion lens and to take out a signal linefrom this electrode to a controlling circuit. This, however, complicatesthe apparatus to render the manufacture of the optical pickup devicedifficult.

On the other hand, the present Applicant has already proposed, in thespecification and drawings of the Japanese patent Application No.H10-249880, a method for detecting the return light from a glass masterdisc and for using thus return light as a gap error signal.

This method exploits the phenomenon in which, if the gap between thesolid immersion lens and the glass master disc is zero, the solidimmersion lens surface is contacted with a transparent photoresist onthe glass master disc, so that there occurs no light reflection from thelens surface, however, if the gap is not zero, the light totallyreflected on the solid immersion lens surface is returned, this lightbeing used for detecting the gap.

This method can be used when the glass master disc is used and thephotoresist for light exposure is transparent. This method, however,cannot be used for a case in which a reflective film, such as analuminum film, a phase change film or a photomagnetic recording film, isformed on the disc surface, as in an optical disc, because the lightthen undergoes reflection on the optical disc surface, even though thegap between the disc and the solid immersion lens is zero.

DISCLOSURE OF THE INVENTION

It is therefore an object of the present invention to provide a noveloptical pickup device and a recording and/or reproducing apparatuscapable of resolving the problems inherent to the above-describedconventional devices.

It is another object of the present invention to provide an opticalpickup device whereby the minute gap between the optical disc having areflective film formed on its surface and the solid immersion lens canbe detected accurately and whereby the gap between the optical disc andthe solid immersion lens can be controlled accurately. It is yet anotherobject of the present invention to provide a recording and/orreproducing apparatus employing the optical pickup device and acontrolling method for controlling the gap.

For accomplishing these objects, the present invention provides anoptical pickup device including an objective lens, with a numericalaperture (NA) being not less than 1, having a solid immersion lens whichis made up by a spherical portion and a flat portion parallel to thesurface of an optical recording medium. The optical pickup deviceincludes a light source for illuminating a light beam of a presetpolarized state through the objective lens to the optical recordingmedium, and photodetector means for detecting the component of the lightreflected back from the optical recording medium in the polarized stateperpendicular to the polarized state of the reflected light whichprevails when the distance between the surface of the optical recordingmedium and the flat portion of the solid immersion lens is zero. Theintensity of light detected by the photodetector means is correlatedwith the distance between the surface of the optical recording mediumand the flat portion of the solid immersion lens.

Preferably, the optical pickup device further includes driving means forcausing movement of the solid immersion lens in a direction towards andaway from the optical recording medium for varying the distance betweenthe surface of the optical recording medium and the flat portion of thesolid immersion lens, and controlling means for controlling the drivingmeans for controlling the position of the solid immersion lens in thedirection towards and away from the optical recording medium. Thecontrolling means operates for maintaining the intensity of lightdetected by the photodetector means to a preset intensity formaintaining the distance between the surface of the optical recordingmedium and the flat portion of the solid immersion lens to a presetvalue.

The present invention also provides a recording and/or reproducingapparatus including medium holding means for holding an opticalrecording medium, and an optical pickup device including an objectivelens, with a numerical aperture (NA) being not less than 1, having asolid immersion lens which is made up by a spherical portion and a flatportion parallel to the surface of an optical recording medium, held bythe medium holding means, a light source for illuminating a light beamof a preset polarized state through the objective lens to the opticalrecording medium, and photodetector means for detecting the component ofthe light reflected back from the optical recording medium in thepolarized state perpendicular to the polarized state of the reflectedlight which prevails when the distance between the surface of theoptical recording medium and the flat portion of the solid immersionlens is zero. The optical pickup device writes or reads out informationsignals for the optical recording medium. The recording and/orreproducing apparatus also includes driving means for causing movementof the solid immersion lens in a direction towards and away from theoptical recording medium for varying the distance between the surface ofthe optical recording medium and the flat portion of the solid immersionlens, and controlling means for controlling the driving means forcontrolling the position of the solid immersion lens in the directiontowards and away from the optical recording medium. The controllingmeans operates for maintaining the intensity of light detected by thephotodetector means to a preset intensity for maintaining the distancebetween the surface of the optical recording medium and the flat portionof the solid immersion lens to a preset value.

The present invention also provides a gap detecting method fordetecting, in an optical pickup device including an objective lens, witha numerical aperture (NA) being not less than 1, having a solidimmersion lens which is made up by a spherical portion and a flatportion extending parallel to the surface of an optical recordingmedium, the distance between the flat portion of the solid immersionlens and the surface of the optical recording medium. The methodincludes illuminating a light beam radiated from a light source of theoptical pickup device through the objective lens to the opticalrecording medium in a preset polarized state, detecting, byphotodetector means of the optical pickup device, the component of thelight beam reflected from the optical recording medium in the polarizedstate perpendicular to the polarized state of the reflected light whichprevails when the distance between the surface of the optical recordingmedium and the flat portion of the solid immersion lens, is zero, andcorrelating the intensity of light detected by the photodetector meanswith the distance between the surface of the optical recording mediumand the flat portion of the solid immersion lens for detecting thedistance between the surface of the optical recording medium and theflat portion of the solid immersion lens.

The present invention also provides a controlling method forcontrolling, in an optical pickup device including an objective lens,with a numerical aperture (NA) being not less than 1, having a solidimmersion lens which is made up by a spherical portion and a flatportion parallel to the surface of an optical recording medium, thedistance between the flat portion of the solid immersion lens and thesurface of the optical recording medium, to a preset value. The methodincludes illuminating a light beam radiated from a light source of theoptical pickup device through the objective lens to the opticalrecording medium in a preset polarized state, detecting, byphotodetector means of the optical pickup device, the component of thelight beam reflected from the optical recording medium in the polarizedstate which is perpendicular to the polarized state of the reflectedlight which prevails when the distance between the surface of theoptical recording medium and the flat portion of the solid immersionlens is zero, moving the solid immersion lens in a direction towards andaway from the optical recording medium, with use of driving means, forvarying the distance between the surface of the optical recording mediumand the flat portion of the solid immersion lens, and controlling thedriving means, using controlling means, for controlling the position ofthe solid immersion lens in the direction towards and away from theoptical recording medium. The controlling means operates for maintainingthe intensity of light detected by the photodetector means to a presetintensity for maintaining the distance between the surface of theoptical recording medium and the flat portion of the solid immersionlens to a preset value.

Other objects, features and advantages of the present invention willbecome more apparent from reading the embodiments of the presentinvention as shown in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing the structure of an optical pickup deviceaccording to the present invention.

FIG. 2A is a graph showing the distribution of an X-component of theelectrical field of an incident light beam on an optical disc in theoptical pickup device, and FIG. 2B is a graph showing the distributionof a Y-component thereof.

FIGS. 3A and 3B are each longitudinal cross-sectional views showing thestate in which a solid immersion lens forming the objective lens of theoptical pickup device is in intimate contact with the optical discsurface.

FIGS. 4A and 4B are each graphs showing the distribution of return lightfrom the optical disc when the solid immersion lens of the opticalpickup device is in intimate contact with the optical disc surface.

FIG. 5 is a longitudinal cross-sectional view showing the state in whichthe solid immersion lens of the optical pickup device is spaced apartfrom the optical disc surface.

FIGS. 6A and 6B are each graphs showing the distribution of return lightfrom the optical disc when the solid immersion lens of the opticalpickup device is spaced apart from the optical disc surface.

FIG. 7 is graph showing the relationship between the distance betweenthe solid immersion lens of the optical pickup device and the opticaldisc surface and gap error signals.

FIG. 8 is a block diagram showing an optical pickup device and arecording and/or reproducing apparatus employing the optical pickupdevice according to the present invention.

FIG. 9 is a side view showing a modification of the optical pickupdevice according to the present invention.

FIG. 10 is a side view showing a further modification of the opticalpickup device according to the present invention.

FIG. 11 is a longitudinal cross-sectional view showing the state inwhich the solid immersion lens of the optical pickup device shown inFIG. 10 is in intimate contact with the optical disc surface.

FIGS. 12A and 12B are each graphs showing the distribution of the returnlight from the optical disc when the solid immersion lens of the opticalpickup device shown in FIG. 10 is in intimate contact with the opticaldisc.

FIGS. 13A and 13B are each graphs showing the distribution of the returnlight from the optical disc when the solid immersion lens of the opticalpickup device shown in FIG. 10 is spaced apart from the optical disc.

FIG. 14 is a graph showing the relationship between the distance betweenthe solid immersion lens of the optical pickup device shown in FIG. 10and the optical disc surface and the gap error signals.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to the drawings, certain preferred embodiments of the presentinvention will be explained in detail.

Referring to FIG. 1, an optical pickup device according to the presentinvention comprises an objective lens 2 including a solid immersion lens1, with the numerical aperture (NA) being not less than 1. The solidimmersion lens 1 includes a spherical surface portion 1 a forming aportion of a sphere and a flat portion 1 b facing a surface 101 a of anoptical disc 101 parallel thereto.

A distance (gap) G₁ between the flat portion 1 b of the solid immersionlens 1 forming the objective lens 2 and the surface 101 a of the opticaldisc 101 as an optical recording medium is controlled, by control meansprovided in the optical pickup device according to the presentinvention, so as to be a distance G₁ on the order of one-tenth of thewavelength λ of a light beam radiated from a semiconductor laser 3 as alight source. The optical pickup device of the present invention,controlled in this manner, is used for a recording and/or reproducingapparatus, employing an optical disc as a recording medium. In thisrecording and/or reproducing apparatus, the distance or gap G₁ betweenthe flat portion 1 b of the solid immersion lens 1 forming the objectivelens 2 and the surface 101 a of the optical disc 101 is controlled to bewithin a preset range.

The optical pickup device according to the present invention detects thecomponent of the light, which is radiated from a semiconductor laser 3,illuminated on the optical disc 101 and reflected from the reflectivesurface of the optical disc 101, and which is in a polarized stateperpendicular to the polarized state of the reflected light whichprevails when the distance or gap G₁ between the surface 101 a of theoptical disc 101 and the flat portion 1 b of the solid immersion lens 1,is zero, thereby producing a gap error signal associated with thedistance G₁ between the surface 101 a of the optical disc 101 and theflat portion 1 b of the solid immersion lens 1.

That is, with the optical pickup device according to the presentinvention, a light beam L₁, radiated from the semiconductor laser 3, iscollimated by a collimator lens 4 to fall on a beam splitter 5. Thewavelength of the light beam L₁, radiated from the semiconductor laser3, is e.g., 40 nm. The light beam L₁, radiated from the semiconductorlaser 3, is transmitted through the beam splitter 5 to fall on apolarized beam splitter 6. The light beam L₁, radiated from thesemiconductor laser 3, is the P-polarized light with respect to thereflective surface of the polarized beam splitter 6, and is transmittedthrough this reflective surface and through the polarized beam splitter6.

The light beam L₁, transmitted through the polarized beam splitter 6, istransmitted through a quarter wave (λ/4) plate 7, having its crystalaxis tilted 45E relative to the direction of the incident polarizedlight, and is thereby turned into the circular polarized light. Thiscircular polarized light then falls on a light condensing lens 8, whichforms the objective lens 2 along with the solid immersion lens 1. Thelight condensing lens 8 converges the incident light beam to cause theconverged light to fall on the solid immersion lens 1. With this solidimmersion lens 1, a converged light point is formed in the vicinity ofthe flat portion 1 b lying proximate and parallel to the surface 101 aof the optical disc 101. The solid immersion lens 1 has a refractiveindex of 1.8, as an example.

The light beam L₁, condensed by the objective lens 2, having the solidimmersion lens 1, is condensed as an evanescent wave on the signalrecording surface 101 a of the optical disc 101. The numerical aperture(NA) of the objective lens 2 in this case is on the order of 1.36.

The optical pickup device of the present invention is used forreproducing information signals recorded on an optical disc, on whichthe information signals have been recorded by a pit pattern of lands andgrooves, or on an optical disc, on which the information signals havebeen recorded by exploiting the phase change. That is, the light beamL₁, radiated from the semiconductor laser 3 provided in the opticalpickup device and condensed by the objective lens 2 so as to beilluminated on the signal recording surface of the optical disc 101, isreflected by this signal recording surface so as to be again incident onthe objective lens 2. A light beam L₂, reflected back from the signalrecording surface of the optical disc 101, is reflected in a variablefashion, depending on e.g., the presence or absence of the pit patternformed on the signal recording surface of the optical disc 101, so as tobe again incident on the objective lens 2. The reflected light L₂,incident on the objective lens 2, is transmitted through the objectivelens 2 and the λ/4 plate 7 to fall on the polarized beam splitter 6.

The reflected light L₂, reflected back from the optical disc 101 towardsthe objective lens 2, is transmitted through the λ/4 plate 7 so as to bethereby turned from the circular polarized light into the linearpolarized light. The direction of polarization in this case isperpendicular to the direction of polarization of the light beam L₁radiated from the semiconductor laser 3. Consequently, the reflectedlight L₂, reflected back from the optical disc 101, is the S-polarizedlight with respect to the reflective surface of the polarized beamsplitter 6. This light beam is reflected by the reflective surface andseparated from the optical path of the return light to the semiconductorlaser 3 so as to be incident on a first detector 9 adapted for detectingthe information signals recorded on the optical disc 101. The firstdetector 9 outputs a detection signal, corresponding to the informationsignals recorded on the optical disc 101, from the detected reflectedlight L₂.

In the optical pickup device of the present invention, the light beamL₁, radiated from the semiconductor laser 3, is the linear polarizedlight having, on a plane A intermediate between the beam splitter 5 andthe polarized beam splitter 6, only the component of the electricalfield of the X-direction, as shown in FIG. 2A, but not having thecomponent of the electrical field of the Y-direction, as shown in FIG.2B.

The solid immersion lens 1, forming the objective lens 2, in the opticalpickup device according to the present invention, is in intimate contactwith the phase change type recording layer or the reflective film,formed on the surface of the optical disc 101, when the flat portion 1 bthereof is in intimate contact with the surface 101 a of the opticaldisc 101.

That is, with the optical disc 101, having a phase change type recordinglayer 107, a first SiO₂ layer 104, a GeSbTe layer 105 and a second SiO₂layer 106 are sequentially deposited on an aluminum layer 103, as areflective layer, deposited on a substrate 102, formed of syntheticresin or glass, to form the recording layer 107, as shown in FIG. 3A.When the solid immersion lens 1, forming the objective lens 2, is inintimate contact with the surface of the phase change optical disc 101,the flat portion 1 b of the solid immersion lens 1 is in intimatecontact with the phase change type recording layer 107, as shown in FIG.3A.

On the other hand, with the optical disc 101, having information signalsrecorded by a pit pattern on one surface of a substrate 110, formed ofsynthetic resin or glass, a reflective film 111 of aluminum is formed tooverlie the pit pattern formed on one surface of the substrate 110, asshown in FIG. 3B. In the case of the optical disc, on which informationsignals have been recorded by this pit pattern, when the solid immersionlens 1, forming the objective lens 2, is in intimate contact with thesurface of the optical disc 101, the flat portion 1 b of the solidimmersion lens 1 is in intimate contact with the reflective film 111, asshown in FIG. 3B.

When the flat portion 1 b of the solid immersion lens 1, forming theobjective lens 2, is in intimate contact with the surface 101 a of theoptical disc 101, as shown in FIGS. 3A and 3B, substantially thetotality of reflected light from the optical disc 101 is reciprocatedthrough the λ/4 plate 7, so that the direction of polarization of thelight is rotated 90E. Thus, on a plane B, directly ahead of the firstdetector 9, the light incident thereon has a distribution approximatelyequal to the distribution of the light beam L₁ radiated from thesemiconductor laser 3, as shown in FIG. 4A. The reflected light L₂ fromthe optical disc 101 is scarcely returned at this time to the plane Alying intermediate the beam splitter 5 and the polarized beam splitter6, as shown in FIG. 4B.

When the solid immersion lens 1 is separated a preset distance D₁ fromthe surface 101 a of the optical disc 101, as shown in FIG. 5, the lightcollected in the vicinity of the flat portion 1 b of the solid immersionlens 1 and which is incident at an angle exceeding the critical angle inthe flat portion 1 b (refractive index of the solid immersion lens nsilH sin(incident angle)>1) is totally reflected on the flat portion 1 b.

When the light L₃, totally reflected on the flat portion 1 b of thesolid immersion lens 1, is totally reflected in this manner on the flatportion 1 b, its direction of polarization undergoes delicate rotation.Thus, the light L₃, totally reflected by the flat portion 1 b of thesolid immersion lens 1, contains a polarized light component which isperpendicular to the reflected light L₂ that is produced when the flatportion 1 b of the solid immersion lens 1 is in intimate contact withthe surface 101 a of the optical disc 101. Consequently, thedistribution of the return light on the plane A, which is the planeintermediate the beam splitter 5 and the polarized beam splitter 6, issuch a one which will be produced when only the rim portion of the lightbeam L₁ radiated from the semiconductor laser 3 is returned, as shown inFIG. 6A.

Thus, the light returned to the plane A intermediate between the beamsplitter 5 and the polarized beam splitter 6, is reflected by thereflective surface of the beam splitter 5, so as to be received by asecond detector 10, which is used for producing a gap error signal, asshown in FIG. 1. This gap error signal is associated with the distanceD₁ between the flat portion 1 b of the solid immersion lens 1 and thesurface 101 a of the optical disc 1.

The distribution of the return light on the plane B, directly ahead ofthe first detector 9, is such a one in which the rim portion of thelight beam L₁ radiated from the semiconductor laser 3 is lacking, asshown in FIG. 6B.

The relationship between the volume of light received by the seconddetector 10 and the distance (air gap) D₁ between the flat portion 1 bof the solid immersion lens 1 and the surface 101 a of the optical disc101 is such that, if, as shown in FIG. 7, the position of the solidimmersion lens 1 in the direction towards and away from the optical disc101 is controlled so that the light volume on the second detector 10will be maintained at a ratio of 0.2 with respect to the incident lightvolume, the distance D₁ (air gap) may be kept at one-tenth of thewavelength λ of the light beam used.

The optical pickup device of the present invention includes a controldevice for maintaining the distance D₁ between the surface 101 a of theoptical disc 101 and the flat portion 1 b of the solid immersion lens 1at a preset value. This control device includes a voice coil motor 20,forming a driving mechanism for causing movement of the solid immersionlens 1 in a direction towards and away from the optical disc 101, adriving circuit 21 for driving the motor 20 and a control circuit 22forming a controller for controlling the driving circuit 21, as shown inFIG. 8. The driving circuit 21 drives the voice coil motor 20 to controlthe distance D₁ between the surface 111 a of the optical disc 101 andthe flat portion 1 b of the solid immersion lens 1. The control circuit22 causes the driving circuit 21 to control the position of the solidimmersion lens 1 in a direction towards and away from the optical disc101, indicated by arrows Y1 and Y2 in FIG. 8, to maintain the intensityof light detected by the second detector 10 at a preset intensity,thereby performing control to maintain the distance D₁ between thesurface 101 a of the optical disc 101 and the flat portion 1 b of thesolid immersion lens 1 at a preset value.

For maintaining the light intensity, as detected by the second detector10, at a preset value, the output signal of the second detector 10 iscompared by a comparator 23 to a preset reference value. For determiningthis reference value, the following methods may be used.

The first method is such a one in which an average value of an output ofthe second detector 10 when the surface 101 a of the optical disc 101 isin intimate contact with the flat portion 1 b of the solid immersionlens 1, that is when the distance D₁ between the surface 101 a of theoptical disc 101 and the flat portion 1 b of the solid immersion lens 1is zero, and an output of the second detector 10 when the distance D₁between the surface 101 a and the flat portion 1 b is sufficientlylarge, is used as the reference value.

The second method is such a one in which the distance D₁ between thesurface 101 a of the optical disc 101 and the flat portion 1 b of thesolid immersion lens 1 is measured by another suitable method and thecorrelation between the measured value and the output of the seconddetector 10 is found to determine an output corresponding to the presetdistance D₁ for use as the reference value.

The third method is such a one in which one-half of the output of thesecond detector 10 in case the distance D₁ between the surface 101 a ofthe optical disc 101 and the flat portion 1 b of the solid immersionlens 1 is sufficiently large is used as the reference value.

Referring to FIG. 8, a recording and/or reproducing apparatus accordingto the present invention, employing the above-described optical pickupdevice, includes a reproducing circuit (reproducing block) 24 formaintaining a preset position relationships between the optical disc 101and the optical pickup device, by providing a supporting mechanism forsupporting the optical disc 101, and for processing signals output fromthe optical pickup device, a recording circuit (recording block) 25 forprocessing signals recorded on the optical disc 101 by this opticalpickup device, and a control circuit 22 for controlling the opticalpickup device. When the optical disc 101 is used as the opticalrecording medium, the supporting mechanism is a spindle mechanism 26including a spindle motor holding the center portion of and rotationallydriving the optical disc.

When the optical pickup device according to the present invention isused in conjunction with a magneto-optical disc 130, as an opticalrecording medium, the light beam L₁, radiated from the semiconductorlaser 3, is condensed on the signal recording surface of themagneto-optical disc 130, after passing through the collimator lens 4,polarized beam splitter 6, beam splitter 5, light condensing lens 8 andthe solid immersion lens 1, as shown in FIG. 9. In the present opticalpickup device, no λ/4 plate is provided on the forward optical path onwhich the light beam L₁ radiated from the semiconductor laser 3 travelsto fall on the magneto-optical disc 130.

The reflected light L₂, reflected back from the magneto-optical disc130, is separated by the beam splitter 5 and is then transmitted througha λ/2 plate 11, operating as a rotatory polarizer, whereby the directionof polarization is rotated 45E. The resulting light then is incident ona second polarized beam splitter 12. The λ/2 plate 11 is arranged withits optical axis tilted at an angle of 22.5E relative to the directionof polarization of the incident linear polarized light.

When reflected by the signal recording surface of the magneto-opticaldisc 130, the reflected light L₂, incident on the second polarized beamsplitter 12, is separated in dependence upon the Kerr rotating angleresulting from the photomagnetic effect so as to be received by a firstdetector 13 and a second detector 14 for generating photomagneticsignals. A difference signal between the output signals of the first andsecond detectors 13, 14, which becomes zero when the reflected light L₂is not subjected to Kerr rotation, is detected as an outputcorresponding to the Kerr rotation angle, generated in the reflectedlight L₂, so as to be used as a photomagnetic signal.

The return light L₃ for producing a gap error signal, reflected backfrom the flat portion 1 b of the solid immersion lens 1, is transmittedthrough the beam splitter 5 and returned to the polarized beam splitter6. The return light is then reflected by the polarized beam splitter 6and received by the third detector 10 used for producing the gap errorsignal.

If the magneto-optical disc 130 is used as an optical recording medium,the optical pickup device according to the present invention may bedesigned so that the light beam L₁ radiated from the semiconductor laser3 is condensed on the signal recording surface of the magneto-opticaldisc 130 after passing through the collimator lens 4, beam splitter 5,condensing lens 8 and the solid immersion lens 1, as shown in FIG. 10.

The light beam L₁, illuminated on the signal recording surface of themagneto-optical disc 130, is reflected by this signal recording surfaceand proves to be a return light beam L₂, which is reflected by the beamsplitter 5 and separated by a second beam splitter 15 into two lightbeams L₄ and L₅. The light beam L₄, transmitted through the second beamsplitter 15, is transmitted through the λ/2 plate 11 and has itsdirection of polarization rotated 45E to fall on the polarized beamsplitter 12. The λ/2 plate 11 is mounted at an angle of tilt of 22.5Ewith respect to the direction of the incident linear polarized light.

When reflected on the signal recording surface of the magneto-opticaldisc 130, the light incident on the polarized beam splitter 12 isseparated, in dependence upon the Kerr rotation angle produced under thephotomagnetic effect, so as to be received by the first and seconddetectors 13 and 14, adapted for producing photomagnetic signals: Adifference signal between the output signals of the first and seconddetectors 13, 14, which becomes zero when the reflected light is notsubjected to Kerr rotation, is detected as an output corresponding tothe Kerr rotation angle generated in the reflected light, so as to beused as a photomagnetic signal.

The light beam reflected by the second beam splitter 15 is incident on asecond polarized beam splitter 16. A fraction of this light beam, usedfor obtaining the gap error signal, and which has been returned from theflat portion of the solid immersion lens 1, is reflected by the secondpolarized beam splitter 16 so as to be received by the third detector 10designed for producing the gap error signal.

In the present optical pickup device, as in the optical system shown inFIG. 1, the state of polarization of the light incident on the beamsplitter 5 is such that the incident light is the linear polarized lighthaving only the electrical field component in the X-direction, as shownin FIG. 2A, but not having the electrical field component in theY-direction, as shown in FIG. 2B. The respective beam splitters 5, 15transmit and reflect equal amounts of the polarized light components inthe X- and Y-directions.

When the optical pickup device shown in FIG. 10 is used for the opticaldisc 101 having the phase change type recording layer, the flat portion1 b of the solid immersion lens 1 forming the objective lens 2 isintimately contacted with the surface 101 a of the optical disc 101. Theflat portion 1 b of the solid immersion lens 1 is intimately contactedat this time with a recording layer 117, formed on one surface of asubstrate 112 of the optical disc 101, as shown in FIG. 11. Therecording layer 117, provided on the optical disc 101, shown in FIG. 11,is formed by sequentially layering a first SiO₂ layer 114, a TeFeColayer 115 and a second SiO₂ layer 116, on an aluminum layer 113,provided on a substrate 112 of synthetic resin or glass, for forming areflective film.

When the flat portion 1 b of the solid immersion lens 1 of the opticalpickup device, shown in FIG. 10, is intimately contacted with thesurface 101 a of the optical disc 101, the distribution of the returnlight on the plane B, which the light reaches after transmission throughthe second polarized beam splitter 16, is approximately equal to that ofthe outgoing light from the semiconductor laser 3, as shown in FIG. 12A.There is scarcely any light returned from the optical disc 101 to theplane C which lies directly ahead of the third detector 10 on whichfalls the light reflected by the second polarized beam splitter 16, asshown in FIG. 12B. Thus, when the flat portion 1 b of the solidimmersion lens 1 is in intimate contact with the surface 101 a of theoptical disc 101, the return light on the plane C is practically nil,such that the reflected light scarcely reaches the third detector 10.

When the solid immersion lens 1 is separated from the optical disc 101,the light collected in the vicinity of the flat portion 1 b of the solidimmersion lens 1 and which is incident at an angle exceeding thecritical angle in the flat portion 1 b (refractive index of the solidimmersion lens nsil H sin(incident angle)>1) is totally reflected on theflat portion 1 b, as shown in FIG. 5.

When the light totally reflected on the flat portion 1 b of the solidimmersion lens 1 is totally reflected in this manner on the flat portion1 b, its direction of polarization undergoes delicate rotation. Thus,the light, totally reflected by the flat portion 1 b of the solidimmersion lens 1, contains a polarized light component which isperpendicular to the reflected light that is produced when the flatportion 1 b of the solid immersion lens 1 is intimately contacted withthe surface 101 a of the optical disc 101. Consequently, thedistribution of the return light on the plane C, lying directly ahead ofthe third detector 10, on the path of light reflected by the secondpolarized beam splitter 16 to fall on the third detector 10, is such aone in which part of the rim of the light beam has been returned, asshown in FIG. 13B.

The light returned to the plane C in this manner is received by thethird detector 10, adapted for producing the gap error signal. This gaperror signal is a signal associated with the distance D₁ between theflat portion 1 b of the solid immersion lens 1 and the surface 101 a ofthe optical disc 101.

At this time, the light distribution on the plane B, which the lighttransmitted through the second polarized beam splitter 16 reaches, issuch a one in which the portion corresponding to the rim of the lightbeam is lacking, as shown in FIG. 13A.

As for the relationship between the light volume received by the thirddetector 10 and the distance D₁ (air gap) between the flat portion 1 bof the solid immersion lens 1 and the surface 110 a of the optical disc101, the distance D₁ (air gap) can be maintained to one-tenth of thewavelength by controlling the position along the direction towards andaway from the optical disc 101 of the solid immersion lens 1, as shownin FIG. 14, so that the light volume on the third detector 10 will bemaintained at one-tenth of the incident light volume.

In the above-described respective optical pickup devices, theexplanation on the optical system for tracking error detection isomitted. However, any suitable optical systems for tracking errordetection may be provided to detect tracking error signals to effecttracking error control for the objective lens.

INDUSTRIAL APPLICABILITY

As described above, the present invention provides an optical pickupdevice having an objective lens, with the numerical aperture not lessthan 1, including a solid immersion lens having a spherical portion anda flat portion parallel to the surface of an optical recording medium,in which the component of the reflected light in the polarized statefrom the optical recording medium which is perpendicular to thepolarized state of the reflected light which prevails when the distancebetween the surface of the optical recording medium and the flat portionof the solid immersion lens is zero, is detected, and the distancebetween the surface of the optical recording medium and the flat portionof the solid immersion lens is detected from the detected lightintensity, so that the minute gap between the optical recording mediumand the solid immersion lens can be detected accurately.

1. An optical pickup device including an objective lens, with anumerical aperture (NA) not being less than 1, having a solid immersionlens which has a spherical portion and a flat portion parallel to thesurface of an optical recording medium, said optical pickup devicecomprising: a light source configured to illuminate a light beam of apreset polarized state through said objective lens to said opticalrecording medium; and a photodetector configured to detect the componentof the light reflected back from said optical recording medium in thepolarized state perpendicular to the polarized state of the reflectedlight which prevails when the distance between the surface of saidoptical recording medium and said flat portion of said solid immersionlens is zero, the intensity of light detected by said photodetectorbeing associated with the distance between the surface of said opticalrecording medium and said flat portion of said solid immersion lens. 2.The optical pickup device according to claim 1 further comprising: anactuator configured to cause movement of said solid immersion lens in adirection towards and away from said optical recording medium to varythe distance between the surface of the optical recording medium andsaid flat portion of said solid immersion lens; and controllingcircuitry configured to control said actuator for controlling theposition of said solid immersion lens in the direction towards and awayfrom said optical recording medium, said controlling circuitrymaintaining the intensity of light detected by said photodetector to apreset intensity for maintaining the distance between the surface of theoptical recording medium and the flat portion of the sold immersion lensto a preset value.
 3. A recording and/or reproducing apparatuscomprising: a medium holding device configured to hold an opticalrecording medium; an optical pickup device including an objective lens,with a numerical aperture (NA) not being less than 1, having a solidimmersion lens which has a spherical portion and a flat portionextending parallel to the surface of an optical recording medium, heldby said medium holding device, a light source for illuminating a lightbeam of a preset polarized state through said objective lens to saidoptical recording medium, and a photodetector configured to detect thecomponent of the light reflected back from said optical recording mediumin the polarized state perpendicular to the polarized state of thereflected light which prevails when the distance between the surface ofsaid optical recording medium and said flat portion of said solidimmersion lens is zero, said optical pickup device writing or readingout information signals for said optical recording medium; an actuatorconfigured to cause movement of said solid immersion lens in a directiontowards and away from said optical recording medium to vary the distancebetween the surface of the optical recording medium and said flatportion of said solid immersion lens; and controlling circuitryconfigured to control said actuator for controlling the position of saidsolid immersion lens in the direction towards and away from said opticalrecording medium, said controlling circuitry maintaining the intensityof light detected by said photodetector to a preset intensity formaintaining the distance between the surface of the optical recordingmedium and the flat portion of the solid immersion lens to a presetvalue.
 4. The optical pickup device according to claim 1, furthercomprising: a second photodetector configured to detect the informationsignal recorded on the optical recording medium and output a detectionsignal corresponding to the information signals recorded on the opticalrecording medium.
 5. The optical pickup device according to claim 3,further comprising: a second photodetector configured to detect theinformation signal recorded on the optical recording medium and output adetection signal corresponding to the information signals recorded onthe optical recording medium.
 6. A method of detecting a distancebetween two objects, comprising: illuminating a light beam of a presetpolarized state through an objective lens of an optical pickup device toan optical recording medium, the objective lens has a numerical aperture(NA) not less than 1 and includes a solid immersion lens which has aspherical portion and a flat portion parallel to a surface of theoptical recording medium; detecting a component of light reflected backfrom said optical recording medium in the polarized state perpendicularto the polarized state of the reflected light which prevails when thedistance between the surface of said optical recording medium and saidflat portion of said solid immersion lens is zero, the intensity oflight detected by said photodetector being associated with the distancebetween the surface of said optical recording medium and said flatportion of said solid immersion lens.
 7. The method of claim 6, furthercomprising: moving said solid immersion lens in a direction towards andaway from said optical recording medium to vary the distance between thesurface of the optical recording medium and said flat portion of saidsolid immersion lens; and controlling said actuator for controlling theposition of said solid immersion lens in a direction towards and awayfrom said optical recording medium, and maintaining the intensity oflight detected by said photodetector to a preset intensity formaintaining the distance between the surface of the optical recordingmedium and the flat portion of the sold immersion lens to a presetvalue.
 8. A method of detecting a distance between two objects,comprising: holding an optical recording medium; illuminating a lightbeam of a preset polarized state through an objective lens of an opticalpickup device to said optical recording medium, the objective lenshaving a numerical aperture (NA) not less than 1 and having a solidimmersion lens which has a spherical portion and a flat portionextending parallel to a surface of the optical recording medium;detecting a component of light reflected back from said opticalrecording medium in the polarized state perpendicular to the polarizedstate of the reflected light which prevails when a distance between thesurface of said optical recording medium and said flat portion of saidsolid immersion lens is zero, said optical pickup device writing orreading out information signals for said optical recording medium;moving of said solid immersion lens in a direction towards and away fromsaid optical recording medium to vary the distance between the surfaceof the optical recording medium and said flat portion of said solidimmersion lens; and controlling said actuator for controlling theposition of said solid immersion lens in the direction towards and awayfrom said optical recording medium, and maintaining the intensity oflight detected by said photodetector to a preset intensity formaintaining the distance between the surface of the optical recordingmedium and the flat portion of the solid immersion lens to a presetvalue.